Four people have been charged with smuggling live scorpions into Queenstown from Australia.

Ministry of Primary Industries investigators charged the men with breaches of the Biosecurity Act after six black rock scorpions were allegedly smuggled from Australia through Christchurch International Airport and then into Queenstown.

The four-month biosecurity investigation started in April and was codenamed Operation Rock.

Three defendants are expected to appear in Queenstown District Court on October 7 and the other defendant in Christchurch District Court.

The ministry said it received information that a Queenstown man was in possession of a scorpion in April. A search was conducted and a live scorpion was discovered.

Further investigations suggested there were more scorpions and searches were carried out at two addresses in Queenstown and Arrowtown.

"Questioning of the defendants during the searches indicated that a total of four men were involved in the alleged smuggling ring and that all of the scorpions had been destroyed. The ministry is satisfied that all of the smuggled scorpions have been accounted for," the ministry said.

Scorpions are restricted organisms as defined by the Biosecurity Act 1993. The maximum penalty for each of the charges faced by the men is five years' jail or a fine up to $100,000.

MPI South Island compliance manager John Slaughter said the alleged offending was up there with the worst of its kind and could have had serious biosecurity implications, had the scorpions escaped.

"Illegally introduced organisms can have major consequences for native species of all types if they compete or prey upon native species. In the very worst case scenario, an illegally introduced organism could have truly catastrophic effects on New Zealand's primary and tourism industries.

"We have expert advice that these scorpions could survive in the New Zealand climate, so it's safe to say that we view this as an exceptionally stupid thing to do."